Rotary crosscutters which cut the web delivered from high-speed web printing press, deliver horizontal sheets traveling at high velocity one at a time in end-to-end relationship and requiring stopping and piling for transport. Other equipment may also provide a corresponding delivery of flexible sheets requiring piling.
Such sheets have been delivered between horizontal high-speed conveyor belts which feed the sheets to a lower level horizontal comparatively low speed conveyor belt, with the sheets overlapping each other to compensate for the different traveling speeds involved. For the overlapping action, the trailing ends of the sheets are blown downwardly as they are fed to the low speed belt so that each succeeding sheet can overlap each preceding sheet. The intent is to reduce the sheets' traveling velocity so that without damage the sheets leading edges can strike an abutment beyond the end of the slow speed belt and fall one on top of another to form the pile.
The above technique has the disadvantage that neat piling is difficult or impossible to achieve when the sheets are delivered at high velocity and in closely interspaced end-to-end relationship, because it is a practical impossibility to keep the blowing air, which should act only on the trailing end of a preceding sheet, from blowing down the front end of a succeeding sheet. Another disadvantage is that the possible overlapping of the sheets does not permit operation of the low speed belt at a velocity low enough to positively prevent damage as the sheets' leading edges strike the abutment halting their travel.
With the intent of overcoming those disadvantages, such sheets have been delivered via pneumatic suspension bars which blow air over the tops of the sheets so that the sheets float spaced beneath the bars, with the sheets traveling as described at high velocity. A suction drum rotating at comparatively slow speed below the suspension bars slows each sheet by the sheet's trailing end being depressed into contact with the drum by depressing means positioned above the suspension bars and working downwardly between them. By appropriate timing mechanism, the trailing end of each sheet is pressed down on the suction drum which sucks only via an upper segment, the sheet being thus slowed and then released from the drum so that preceding sheets are overlapped by succeeding sheets.
However, when the sheets have lengths in the range of several meters and are delivered at high velocity, especially if heavy, impregnated or varnished sheets are involved, and such sheets must overlap each other over several meters for the piling, the rotary suction drum concept has substantial disadvantages, especially if electrostatic charges cause the sheets to tend to stick together. In particular, the depressing means cannot depress the trailing sheet ends and quickly enough get out of the way of the leading sheet ends of the overlapping sheets, and the suction drum cannot adequately grip and hold back the overlapped sheets.
The object of the present invention is to provide an improved sheet piler for the sheets traveling at high velocity one at a time and in end-to-end relationship beneath the horizontal suspension bars of the kind described, and which operates more effectively when the sheets are long, such as in the area of several meters long, and are possibly heavily impregnated or varnished.